I built a new upper for suppressed use using the Sionics 11.5” reduced gas port barrel. I function tested today unsuppressed (suppressor still in NFA jail) running a BCM bolt with LMT E-Carrier and Vltor A5 RE, Sprinco green spring and A5H2 buffer. Test was run on a Seekins forged lower with 2500+ rounds run. First 40 rounds through went with no issue. GECO 223 55gr FMJ was fired on approximate 2 second intervals.
Next, I ran some basic movement drills shooting at a much faster pace. IMI 556 55gr FMJ, Wolf Gold 223 55gr FMJ and American Eagle 223 55gr FMJ were used in various Gen 2 and Gen 3, 30 round pmags that have run hundreds of rounds with out issue.
About four to five mags into these drills, as the gun got hot, I started to get failure to extract malfunctions. The first failure to extract was with IMI 556, the remainder of the malfunctions were with the AE 223 rounds.
I was anticipating possible short stroking/failure to lock, but this malfunction doesn’t appear to be that. I changed out the BCM/LMT BCG to a BCM built BCG with several hundred rounds run and the malfunction appeared to go away, however, I was out of the AE ammo after running 20 rounds. Wolf Gold and GECO ran with out issue using the BCM BCG. The ejection pattern with both BCG's was consistent and about 4 o'clock.
Outside air temperature was 87 degrees.
Need some advice on what changes to make to isolate the issue. I don’t think there is a gas flow issue at the gas block, as the barrel is pre-drilled and a BCM low profile gas block with set screws was used and appears to be installed properly. Similar situation with the gas tube.
Thank you.
Nightchief
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